The problem of treatment of wastewater contaminated with volatile organic or inorganic compounds becomes very pressing for many facilities and for many branches of industry. In some cases, volatile organic and inorganic compounds present a major contributor to overall pollution in a facility.
There are different methods of volatile organic and inorganic compounds control in wastewater.
Detailed review of these methods is presented in the article: Victor H. Edwards “VOC-Control Options During Wastewater Treatment” CHEMICAL ENGINEERING, September 2000, pp. 105÷108.
According to this article, all methods of control of volatile organic and inorganic compounds in wastewater can be classified under two main types: 1) with transfer of volatile organic and inorganic compounds from wastewater into vapor phase by distillation, air stripping, steam stripping, inert-gas stripping, fuel-gas stripping, vacuum distillation and vacuum stripping; 2) with transfer of volatile organic and inorganic compounds into a liquid or solid phase: solvent extraction, liquid ion exchange, reverse osmosis, adsorption, ion exchange and precipitation.
Each aforementioned method is distinguished by its advantages and drawbacks.
In the case of application of air stripping related to the first group, this method should be combined with an additional method for treating air laden with volatile organic and inorganic compounds. There are several physicochemical methods of such additional treatment: flare, feed to a furnace or boiler, feed in a thermal or catalytic incinerator, condensation, cryogenic condensation, adsorption using activated carbon, alumina or zeolites.
Each of these additional methods has in turn several advantages and disadvantage related to its cost, efficiency, reliability and safety. As it is known from technical literature (see, for example, “THERMAL AND THERMO-CATALYTIC TREATMENT OF WASTE GASES” Naukova Dumka, 1984, pp. 17÷22 (in Russian)), thermal method of oxidation of waste gases requires about of 26÷45 kg of liquid fuel per 1000 m3 of waste gases and the thermo-catalytic method—15÷25 kg of liquid fuel correspondingly. It is clear, that higher concentration of volatile organic and inorganic compounds in the volatile organic and inorganic compounds-laden air after the air stripping process causes diminishment of a liquid or gaseous fuel required for thermal or thermo-catalytic oxidation of volatile organic and inorganic compounds presented in the wastewater.
In order to achieve higher concentration of volatile organic and inorganic compounds in the volatile organic and inorganic compounds-laden air it is possible to perform the air stripping process with a stage of previous heating wastewater in a heat exchanging unit, it allows achieving higher concentration of volatile organic and inorganic compounds in air after stripping process and, on the other hand, to treat wastewater containing volatile organic compounds with relatively high temperature of boiling at the atmospheric pressure.
In addition, the rate of stripping at elevated temperature is substantially higher, i.e. for the same size of an air-stripping tower, it is possible to treat greater amount of wastewater in the same period.
However, the common process of air stripping at elevated temperature is characterized by great heat losses at the expense of enhanced water evaporation into the volatile organic and inorganic compounds-laden air. As a result, energy cost for wastewater treatment by air stripping at elevated temperatures is very high.